1. Technical Field
The present invention relates in general to an improved welding technique, and in particular to an improved part interface design and method for laser spot welding materials that are difficult to weld together.
2. Description of the Prior Art
Generally, a data access and storage system consists of one or more storage devices that store data on magnetic or optical storage media. For example, a magnetic storage device is known as a direct access storage device (DASD) or a hard disk drive (HDD) and includes one or more disks and a disk controller to manage local operations concerning the disks. The hard disks themselves are usually made of aluminum alloy or a mixture of glass and ceramic, and are covered with a magnetic coating. Typically, one to six disks are stacked vertically on a common spindle that is turned by a disk drive motor at several thousand revolutions per minute (rpm).
A typical HDD also utilizes an actuator assembly. The actuator moves magnetic read/write heads to the desired location on the rotating disk so as to write information to or read data from that location. Within most HDDs, the magnetic read/write head is mounted on a slider. A slider generally serves to mechanically support the head and any electrical connections between the head and the rest of the disk drive system. The slider is aerodynamically shaped to glide over moving air in order to maintain a uniform distance from the surface of the rotating disk, thereby preventing the head from undesirably contacting the disk.
Typically, a slider is formed with an aerodynamic pattern of protrusions on its air bearing surface (ABS) that enables the slider to fly at a constant height close to the disk during operation of the disk drive. A slider is associated with each side of each platter and flies just over the platter""s surface. Each slider is mounted on a suspension to form a head gimbal assembly (HGA). The HGA is then attached to a semi-rigid actuator arm that supports the entire head flying unit. Several semi-rigid arms may be combined to form a single movable unit having either a linear bearing or a rotary pivotal bearing system.
The head and arm assembly (HSA) is linearly or pivotally moved utilizing a magnet/coil structure that is often called a voice coil motor (VCM). The stator of a VCM is mounted to a base plate or casting on which the spindle is also mounted. The base casting with its spindle, actuator VCM, and internal filtration system is then enclosed with a cover and seal assembly to ensure that no contaminants can enter and adversely affect the reliability of the slider flying over the disk. When current is fed to the motor, the VCM develops force or torque that is substantially proportional to the applied current. The arm acceleration is therefore substantially proportional to the magnitude of the current. As the read/write head approaches a desired track, a reverse polarity signal is applied to the actuator, causing the signal to act as a brake, and ideally causing the read/write head to stop and settle directly over the desired track.
Conventional disk drive components are formed primarily from aluminum and stainless steel materials. Stainless steel components such as suspension flexures, load beams, and mount plates are welded together. In contrast, aluminum components such as combs, covers, and base castings are bolted together due to the difficulty of welding aluminum to aluminum. Bolted joints are expensive, create contamination, and can creep under vibration and temperature variations, and have dynamic variations. Drive components are made of aluminum due to its low cost, good machining and formability, excellent heat transfer, and high stiffness-to-weight ratio. Also, stainless steel to stainless steel welds of suspension components result in localized distorsions that change the flatness of suspension components resulting in higher gain of some dynamic modes. In addition, future disk drives may need to be filled with gases like helium or may need internal pressures that are lower than atmospheric pressure. This will require sealing of the drive from the atmosphere that will need aluminum-to-aluminum seam welding of the drive cover to the base.
As stated above, some disk drive components are normally made of 6061 T6 aluminum or equivalent aluminum alloys. These alloys contain manganese, magnesium, etc., low melting point alloys. Components formed from these low melting point alloys evaporate as the aluminum melts during the welding process. Welding-generated gases are trapped in the welds and contribute to porosity and interfere with homogenous mixing of the molten bodies that form the weld nugget. Typically, porosity due to trapped weld gases is at a maximum and more harmful at the center of the weld interface. For high weld strength, the interface should be free of gas bubbles/porosity. Thus, an improved joining technique and design for disk drive components that overcomes the limitations of the prior art is needed.
One embodiment of a joining technique and design for welding of hard to weld elements of a disk drive suspension is disclosed. One or both parts to be welded are machined, coined, or etched at the weld interface. A small pocket, approximately 10 to 200 xcexcm in depth, is formed in one or both of the parts at weld interface to communicate with the atmosphere to let evaporated material gases escape all around the weld during welding so as to greatly reduce gas bubble trapping in the weld nugget. The pocket also helps in reworkability of the joint by accommodating the sheared weld nugget protruding a small amount above the material surface at interface. The presence of bubbles or a porous consistency reduces the weld strength. For laser welding, if the top part is thick, a depression or pocket is formed therein to control the welded web thickness for fast melting and thorough mixing of top and bottom materials in order to form a strong reliable weld. For resistance spot welding, if both top and bottom materials are thick, it may be necessary to form these pockets in both materials on the electrode contact side to reduce material thickness. The technique utilized in the present invention provides a weld interface design that solves the joint reliability and dynamic variation problems. This technique can be used to attach aluminum-to-aluminum or other materials that are difficult to weld due to porous welds, and to improve weld quality of both spot and seam welds. Typical disk drive applications include elimination of fasteners to join aluminum parts together.
The foregoing and other objects and advantages of the present invention will be apparent to those skilled in the art, in view of the following detailed description of the preferred embodiment of the present invention, taken in conjunction with the appended claims and the accompanying drawings.